1. Field of the Invention
Embodiments of the present invention generally relate to detecting and tracking touch on an illuminated surface.
2. Description of the Related Art
Touch displays are used in many consumer applications (e.g., smart phones, computer displays, medical imaging devices, automotive control displays, etc.) to provide an intuitive user interface. The touch detection technology used in such displays includes electrical capacitance detection, electrical resistance detection, and optical detection. For optical touch detection, one or more imaging sensors and one or more light sources (e.g., one or more infrared cameras and infrared light-emitting diodes (LEDs)) may be used to capture images of a touch surface. The captured images are processed to detect objects (e.g., a finger or a stylus) touching or near the surface.
Examples of such optical touch detection systems include an infrared (IR) rear-projection touch system, an IR curtain touch system, and a frustrated total internal reflection system. A typical IR rear-projection touch system includes a projector, a display screen (also referred to as a touch screen or touch surface), infra-red emitters (e.g., LEDs), one or more infra-red sensors (e.g., cameras), and a processing engine. The IR emitters flood the rear surface of the display screen with IR light. Some portion of the IR light rays passes through (refracts) the display screen while the remaining light bounces off (reflects) the screen. The IR camera or cameras create an image from the IR light that makes it back to the sensor. When an object touches the screen, it reflects some of the IR light rays emerging from the screen back through the screen surface toward the IR sensor. The images captured by the camera are analyzed to detect the presence and location (x, y coordinates) of the touch.
In an IR curtain touch system, a curtain of IR light is cast over the touch surface such that the plane of the IR curtain is close to and parallel to the surface while not actually touching the surface. When an object touches the surface, the object breaks the light curtain and IR light reflects off the object. Some of this reflected light is captured by one or more IR cameras located on the same side of the touch surface as the light curtain. The IR camera or cameras create an image from the IR light that makes it back to the sensor. The images captured by the camera are analyzed to detect the presence and location (x, y coordinates) of the touch.
In a frustrated total internal reflection system, one or more IR light sources flood the inside of the screen with infrared light based on the principle of total internal reflection. This light undergoes complete reflections off either surface of the screen and remains trapped inside the material of the screen (usually, acrylic). When a user touches the screen, some of the light rays at the point of contact, instead of being fully reflected, pass through the surface and reflect off the contact material (usually, the user's skin). This frustrated light is then scattered down, away from the contact point, through the screen, and toward an IR camera, which creates an image from the IR light impinging a sensor or sensors in the camera. These light rays create a bright spot on the otherwise dark image. The images thus captured by the camera are analyzed to detect the presence and location of the touch point. In a frustrated total internal reflection system, typically the projector and IR camera are placed behind the screen, opposite from the side from which the user interacts with the screen. However, it is also feasible to place the projector in the front of the screen, on the same side where the user interaction occurs.